Multi-functional peripherals (MFPs) are used to produce digital color copies and to print color documents. MFPs typically generate copies of a document at a slower rate than the rate for printing an original document, because the MFP does not know which portions of the document contain black (e.g., text) and which portions include color (e.g., graphics and photos). Generally, MFPs use multiple color ink cartridges that provide several ink colors (e.g., cyan, magenta, yellow and black). A typical MFP color copying process begins by scanning the document to be copied. With reference to FIG. 1A, the typical document 10 contains red-green-blue (RGB) color images 14 and text 18. The reproduction process includes the step of converting RGB pixel values to cyan-magenta-yellow-black (CMYK) values. The printed copy 10d is the result of four print scans corresponding to the four ink colors. The document 10a resulting from a first print scan includes cyan graphics 14a and cyan text 18a. The next scan deposits magenta ink as depicted in document 10b. Thus graphics 14b and text 18b include magenta ink and cyan ink. The next scan deposits yellow ink as depicted in document 10c. Graphics 14c and text 18c include yellow, magenta and cyan ink. The fourth scan generates the finished copy 10d of the original document 10 and deposits black ink as depicted in document 10d. The copy document 10d includes cyan, magenta, yellow and black ink.
Typically, the text 18 is pure black and only the graphics 14 contain color. As a result, the time needed to copy the document 10 can be reduced if the MFP can discriminate between text pixels and color pixels. Also, the amount of color ink used would be reduced because the color ink would only be used for printing graphics 14. What is needed is an efficient and accurate method of discriminating between text pixels and graphics pixels.